New Limit on the Permanent Electric Dipole Moment of Xe129 Using He

Abstract

We report results of a new technique to measure the electric dipole moment of 129 Xe with 3 He comagnetometry. Both species are polarized using spin-exchange optical pumping, transferred to a measurement cell, and transported into a magnetically shielded room, where SQUID magnetometers detect free precession in applied electric and magnetic fields. The result from a one week measurement campaign in 2017 and a 2.5 week campaign in 2018, combined with detailed study of systematic effects, is dA( 129 Xe) = (1.4 ± 6.6stat ± 2.0syst) × 10 −28 e cm. This corresponds to an upper limit of |dA( 129 Xe)| < 1.4 × 10 −27 e cm (95% CL), a factor of five more sensitive than the limit set in 2001.Searches for permanent electric dipole moments (EDMs) are a powerful way to investigate beyondstandard-model (BSM) physics. An EDM is a charge asymmetry along the total angular momentum axis of a particle or system and is odd under both parity reversal (P) and time reversal (T). Assuming CPT conservation (C is charge conjugation), an EDM is a direct signal of CP violation (CPV), a condition required to generate the observed baryon asymmetry of the universe [1]. The Standard Model incorporates CPV through the phase in the CKM matrix and the QCD parameterθ. However, the Standard Model alone is insufficient to explain the size of the baryon asymmetry [2]. BSM scenarios that generate the observed baryon asymmetry [3] generally also provide for EDMs larger than the SM estimate, which for 129 Xe is |d A ( 129 Xe) SM | ≈ 5 × 10 −35 e cm [4].EDM measurements have provided constraints on how BSM CPV can enter low-energy physics [4]. Diamagnetic systems such as 129 Xe and 199 Hg are particularly sensitive to CPV nucleon-nucleon interactions that induce a nuclear Schiff moment and CPV semileptonic couplings [7]. While the most precise atomic EDM measurement is from 199 Hg [8], there are theoretical challenges to constraining hadronic CPV parameters from 199 Hg alone, and improved sensitivity to the 129 Xe EDM would tighten these constraints [7,9]. Additionally, recent work has shown that contributions from light-axion-induced CPV are significantly stronger for 129 Xe than for 199

Limits on CP-violating hadronic interactions and proton EDM from paramagnetic molecules

“…However, for the proton EDM our limit (5.1) is just about 20 times weaker than the recent constraint on this parameter |d p | < 5 × 10 −25 e • cm [68] which was based on the measurements on EDM of 199 Hg atom [14]. 6 Remarkably, the constraint (5.1) on the proton EDM is nearly 30 times more stringent than that found in recent 129 Xe EDM experiments [70,71]. This sensitivity of eEDM experiments to hadronic CP -violating parameters is actually very impressive.…”

Polyatomic molecules as quantum sensors for fundamental physics

“…fundamental particles and forces in the hadronic sector, including nucleon dipole moments and CP-violating nuclear forces [1,98]. Other atomic searches include Ra [30,121], Xe [122,123], and Rn [124]. Molecular searches include TlF [27,31,125,126] and RaF [104,105,127], both of which can be laser-cooled.…”

Search for electric dipole moments

“…The latest results from experiments using diamagentic atoms to search for an atomic EDM were reported in 2019 by F. Allmendiger et al [23] d Xe = (−4.7±6.4)×10 −28 e cm and N. Sachdeva et al [18] d Xe = (1.4 ± 6.6 stat ± 2.0 sys ) × 10 −28 e cm. These measurements improve the limits on the underlying CPV parameters g 0,1 π andθ by a factor two and C T by a factor five.…”

“…Elaborate atomic, molecular and nuclear calculations are required to account for these contributions. Similarly, when using diamagnetic atoms like 199 Hg [16] or 129 Xe [18,23] nuclear theory is required to extract the CP-violating parameters at the hadronic level, such as the nucleon EDM and CP-violating pion-nucleon couplings, while atomic theory is needed for the extraction of the scalar and tensor couplings of the electron to the nucleons.…”